A variety of procedures and apparatuses related to single lumen catheter fluid treatment, more particularly blood treatment, have developed since the time of my U.S. Pat. No. 3,756,234, now U.S. Pat. No. Re 29,346. The most successful procedures or apparatuses employ the concept of controlling at least one of opening or closing of the venous or arterial line in response to a high or low pressure value which develops in a closed extracorporeal blood circuit, comprising the arterial line leading from the single lumen catheter, the hemodialyser, hemofilter, hemodiafilter, plasmapheresis device, or ascites device, and the venous line, which venous line normally includes a venous line reservoir or drip chamber, leading back to the single lumen catheter. Most popular are procedures involving opening of the venous line with substantially simultaneous closing of the arterial line in response to a preset higher pressure value which develops in the venous line. These procedures sometimes also involve closing of the venous line with substantially simultaneous opening of the artierial line in response to a preset lower pressure value which develops in the venous line. Generally, the pressure value in the venous line is sensed by sensing pressure in a gaseous cushion above the level of fluid, usually purified or treated blood, in the venous line reservoir. Also known are devices in which closing of the venous line with substantially simultaneous opening of the arterial line is in response to a predetermined or adjustable time increment. Similarly, devices in which closing of the arterial line with subtantially simultaneous opening of the venous line is in response to a predetermined or adjustable time increment are known, which devices may either include means for closing of the venous line with substantially simultaneous opening of the arterial line in response to a preset lower pressure value which develops in the venous line, or may include means for closing of the venous line with substantially simultaneous opening of the arterial line in response to a predetermined or adjustable time increment. The latter type of device, i.e. one in which closing of both the arterial and venous lines is in response to predetermined or adjustable time increments are not contemplated by my U.S. Pat. No. Re 29,346 and indeed have been avoided in further research for the reason that control of single lumen catheter fluid treatment procedures exclusively by timer mechanisms excludes achieving what is considered to be an extremely important advantage. Devices including means for closing of the arterial or venous lines in response to a pressure value which develops in the extracorporeal blood circuit are controlled dependently of a particular condition or status within the extracorporeal blood circuit. In other words, systems including means for controlling closing of the arterial and/or venous lines in response to a pressure value developed in the extracorporeal blood circuit are essentially self-regulating. With the above considerations in mind, and in particular bearing in mind the concept of achieving a self-regulating system, it has now been found that a particular combination of means for controlling closing of venous and arterial lines in a single lumen catheter assembly can achieve substantially improved self-regulation as compared to systems employed in the past. More particularly, it has been observed that self-regulation in a single lumen catheter assembly is not complete if there is not also provided means for controlling closure of the venous line dependently of conditions in the arterial line. This consideration, coupled with the procedure of controlling closure of the arterial line dependently of conditions in the venous line, already known in part from devices such as discussed above, has led to a new and greatly improved method and apparatus useful for controlling the closing of an arterial line with substantially simultaneous opening of a venous line and the closing of said venous line with substantially simultaneous opening of said arterial line, which method and apparatus is the subject of the present invention. An assembly of fluid lines specially adapted for the method and apparatus is also provided by the present invention.
The present invention furthermore includes the consideration that there is little point in closing the venous line whilst there is an adequate quantity of untreated fluid upstream of the fluid treatment device. Similarly, or conversely, there is little point in closing the arterial line with substantially simultaneous opening of the venous line before there is an adequate quantity of treated fluid downstream of the fluid treatment device. It is of importance to bear in mind that time should be optimally employed in single lumen catheter fluid treatment procedures since if treatment time with a single lumen catheter exceeds treatment time with double lumen or dual needle treatment procedures too significantly, the now well-known advantages of some single lumen catheter fluid treatment procedures could be outweighed by such increased fluid treatment time.